The present invention relates to equipment for testing of integrated circuits. More particularly, the present invention relates to a method for shaping lithographically-produced probe elements incorporated into probe cards used in testing of semiconductor integrated circuits.
In semiconductor integrated circuit manufacturing, it is conventional to test the integrated circuits (“IC's”) during manufacturing and prior to shipment to ensure proper operation. Wafer testing is a well-known testing technique commonly used in production testing of wafer-mounted semiconductor IC's, wherein a temporary electrical current is established between automatic test equipment (ATE) and each IC mounted on the wafer to demonstrate proper performance of the IC's. Exemplary components used in wafer testing include an ATE test board, which is a multilayer printed circuit board that is connected to the ATE, and that transfers the test signals back and forth between the ATE and a probe card. An exemplary probe card is a printed circuit board that generally contains several hundred probe needles (or “flexible probes”) positioned to establish electrical contact with a series of connection terminals (or “die contacts”) on the IC wafer.
Known probe cards are available from Kulicke and Soffa Industries, Inc. of Willow Grove, Pa. Certain probe cards comprise a printed circuit board, a probe head having a plurality of flexible probes, and a space transformer which electrically connects the probes to the printed circuit board. The space transformer may comprise a multi-layer ceramic substrate, or alternatively a multi-layer organic substrate.
It is known to produce the plurality of flexible probes using lithographic techniques. For example, U.S. Pat. No. 6,616,966 (Mathier et al.) and U.S. Pat. No. 6,677,245 (Zhou et al.) each disclose lithographic methods of producing flexible probes.
One difficulty in the use of probe cards is that the surfaces of the integrated circuit die contacts or pads which are contacted by the flexible probes are typically formed from metals such as aluminum or copper which tend to oxidize, forming an electrically insulating oxide layer. Such an oxide layer is desirably breached by the flexible probe to establish proper electrical communication between each die contact and each flexible probe. It is thus desirable that the tip of each flexible probe be contoured in such a manner as to promote the ability of the flexible probes to penetrate the oxide layer. However, using conventional lithographic techniques, it is difficult to provide the flexible probe tip with the desired sharp edges best adapted to penetrate the die contact oxide layer.
It would therefore be desirable to provide a method by which the tips of lithographically produced probe elements could be shaped to enhance the ability of the probe element to establish electrical communication with a die contact.